Hepatocyte telomere shortening and senescence are general markers of human liver cirrhosis

Secretome of senescent hepatoma cells modulate immune cell fate by macrophage polarization and neutrophil extracellular traps formation

Presence of dysfunctional senescent hepatocytes is a hallmark feature of liver cirrhosis which finally culminates in liver cancer. We now report the presence of senescent hepatocytes (p21 and p53 positive) in the vicinity of infiltrated immune cells in hepatocellular carcinoma tissue specimens by immunohistochemistry. Hence, we evaluated in vitro, the relevance of senescent hepatoma cells in altering the fate of monocytes and neutrophils by assaying for macrophage polarization and extracellular trap (NETs) formation, respectively. Premature senescence was induced in hepatoma cells (HepG2 and Huh7 cells) by treating cells with doxorubicin. Senescent hepatoma cells showed strong inflammatory phenotype with induced expression of cytokines (IL1β, IL6, IL8 and IL13) as evaluated by flow cytometry. The senescent secretome from hepatoma cells when incubated with healthy monocytes caused it to differentiate predominantly towards M2 fate (CD80^low CD86^low CD163^high CD206^high) when analysed by flow cytometry. This was corroborated by the finding in clinical samples where human hepatocellular carcinoma harbouring senescent hepatocytes showed presence of M2 macrophages, while M1 macrophages were predominant in non-tumorous region. Additionally, the senescent secretome from Huh7 cells enhanced the NETs formation, while HepG2 secretome had an inhibitory effect. In conclusion, the "pro-inflammatory" senescent secretome drives non-inflammatory type M2 macrophage polarization and modulated neutrophil traps which in turn can influence the tumor microenvironment.

Diagnostic Value of hTERT mRNA and in Combination With AFP, AFP-L3%, Des-γ-carboxyprothrombin for Screening of Hepatocellular Carcinoma in Liver Cirrhosis Patients HBV or HCV-Related

Diagnosis of hepatocellular carcinoma (HCC) in early-stage, to give an effective treatment option and improve quality of life for cancer patients, is an important medical mission globally. Combination of AFP with some biomarkers may be more supportive in both diagnosis and screening of HCC, but the range value of these markers can be applied as daily markers were unclearly. In some studies, human telomerase reverse transcriptase (hTERT mRNA) was reported as an advantage marker to diagnose cancer. The present study identified serum of 340 patients that were infected chronic hepatitis B virus or hepatitis C virus and divided in 2 groups including Hepatocellular carcinoma (HCC) and liver cirrhosis (LC) to measure their values of hTERT mRNA, AFP, AFP-L3%, and DCP, as well as combination of them. As a result, the concentration of hTERT mRNA, AFP, AFP-L3%, and DCP in HCC groups were significantly higher than that in LC group (P < .01). For detecting HCC, hTERT mRNA had sensitivity of 88% and specificity of 96% (at the cutoff value of 31.5 copies/mL), AFP sensitivity of 73% and specificity of 92% (at the cutoff value of 5.1 ng/mL), AFP-L3% sensitivity of 69% and specificity of 90% (at the cutoff value of 1.05%), DCP sensitivity of 82% and specificity of 92% (at the cutoff value of 29.01 mAU/mL). The largest area under the curve (AUC) of combination hTERT mRNA with DCP was 0.932 (sensitivity of 98.2% and specificity of 88.2%). New combination of DCP with hTERT mRNA gave a useful choice for screening of HCC in chronic HBV or HCV patients associated liver cirrhosis.

Senescence Connects Autophagy Deficiency to Inflammation and Tumor Progression in the Liver

BACKGROUND & AIMS

Cellular senescence frequently is present in injured livers. The induction mechanism and the pathologic role are not always clear. We aimed to understand the dynamics of senescence induction and progression, and the mechanism responsible for the pathology using a mouse model that disables the essential process of autophagy.

METHODS

Mice deficient in key autophagy genes Atg7 or Atg5 in the liver were used. Senescence was measured using established cellular and molecular signatures. The mechanistic roles of nuclear factor erythroid 2 (NRF2), forkhead box K1, and C-C motif chemokine receptor 2 (CCR2) were assessed using mouse genetic models. Liver functions, pathology, and tumor development were measured using biochemical and histologic approaches.

RESULTS

Inducible deletion of Atg7 rapidly up-regulated cyclin-dependent kinase inhibitors independently of injury and induced senescence-associated β-galactosidase activities and senescence-associated secretory phenotype (SASP). Sustained activation of NRF2 was the major factor causing senescence by mediating oxidative DNA damage and up-regulating C-C motif chemokine ligand 2, a key component of autophagy-related SASP, via the NRF2-forkhead box K1 axis. Senescence was responsible for hepatic inflammation through CCR2-mediated recruitment of CD11b⁺ monocytes and CD3⁺ T cells. The CCR2-mediated process in turn enhanced senescence and SASP by up-regulating cyclin-dependent kinase inhibitors and chemokines. Thus, senescence and inflammation can mutually augment each other, forming an amplification loop for both events. The CCR2-mediated process also modulated liver injury and tumor progression at the later stage of autophagy deficiency-related pathology.

CONCLUSIONS

These results provide the insight that hepatic senescence can occur early in the disease process, triggers inflammation and is enhanced by inflammation, and has long-term effects on liver injury and tumor progression.

Hepatitis C Virus Nonstructural 5A Protein Interacts with Telomere Length Regulation Protein: Implications for Telomere Shortening in Patients Infected with HCV

Hepatitis C virus (HCV) is a major cause of chronic liver disease and is highly dependent on cellular proteins for viral propagation. Using protein microarray analysis, we identified 90 cellular proteins as HCV nonstructural 5A (NS5A) interacting partners, and selected telomere length regulation protein (TEN1) for further study. TEN1 forms a heterotrimeric complex with CTC and STN1, which is essential for telomere protection and maintenance. Telomere length decreases in patients with active HCV, chronic liver disease, and hepatocellular carcinoma. However, the molecular mechanism of telomere length shortening in HCV-associated disease is largely unknown. In the present study, protein interactions between NS5A and TEN1 were confirmed by immunoprecipitation assays. Silencing of TEN1 reduced both viral RNA and protein expression levels of HCV, while ectopic expression of the siRNA-resistant TEN1 recovered the viral protein level, suggesting that TEN1 was specifically required for HCV propagation. Importantly, we found that TEN1 is re-localized from the nucleus to the cytoplasm in HCV-infected cells. These data suggest that HCV exploits TEN1 to promote viral propagation and that telomere protection is compromised in HCV-infected cells. Overall, our findings provide mechanistic insight into the telomere shortening in HCV-infected cells.

The Bright and the Dark Side of TGF-β Signaling in Hepatocellular Carcinoma: Mechanisms, Dysregulation, and Therapeutic Implications

Simple Summary

Transforming growth factor β (TGF-β) signaling is a preeminent regulator of diverse cellular and physiological processes. Frequent dysregulation of TGF-β signaling has been implicated in cancer. In hepatocellular carcinoma (HCC), the most prevalent form of primary liver cancer, the autocrine and paracrine effects of TGF-β have paradoxical implications. While acting as a potent tumor suppressor pathway in the early stages of malignancy, TGF-β diverts to a promoter of tumor progression in the late stages, reflecting its bright and dark natures, respectively. Within this context, targeting TGF-β represents a promising therapeutic option for HCC treatment. We discuss here the molecular properties of TGF-β signaling in HCC, attempting to provide an overview of its effects on tumor cells and the stroma. We also seek to evaluate the dysregulation mechanisms that mediate the functional switch of TGF-β from a tumor suppressor to a pro-tumorigenic signal. Finally, we reconcile its biphasic nature with the therapeutic implications.

Abstract

Hepatocellular carcinoma (HCC) is associated with genetic and nongenetic aberrations that impact multiple genes and pathways, including the frequently dysregulated transforming growth factor β (TGF-β) signaling pathway. The regulatory cytokine TGF-β and its signaling effectors govern a broad spectrum of spatiotemporally regulated molecular and cellular responses, yet paradoxically have dual and opposing roles in HCC progression. In the early stages of tumorigenesis, TGF-β signaling enforces profound tumor-suppressive effects, primarily by inducing cell cycle arrest, cellular senescence, autophagy, and apoptosis. However, as the tumor advances in malignant progression, TGF-β functionally switches to a pro-tumorigenic signal, eliciting aggressive tumor traits, such as epithelial–mesenchymal transition, tumor microenvironment remodeling, and immune evasion of cancer cells. On this account, the inhibition of TGF-β signaling is recognized as a promising therapeutic strategy for advanced HCC. In this review, we evaluate the functions and mechanisms of TGF-β signaling and relate its complex and pleiotropic biology to HCC pathophysiology, attempting to provide a detailed perspective on the molecular determinants underlying its functional diversion. We also address the therapeutic implications of the dichotomous nature of TGF-β signaling and highlight the rationale for targeting this pathway for HCC treatment, alone or in combination with other agents.

Telomere dysfunction in ageing and age-related diseases

Ageing organisms accumulate senescent cells that are thought to contribute to body dysfunction. Telomere shortening and damage are recognized causes of cellular senescence and ageing. Several human conditions associated with normal ageing are precipitated by accelerated telomere dysfunction. Here, we systematize a large body of evidence and propose a coherent perspective to recognize the broad contribution of telomeric dysfunction to human pathologies.

Aging reduces liver resiliency by dysregulating Hedgehog signaling

Older age is a major risk factor for damage to many tissues, including liver. Aging undermines resiliency and impairs liver regeneration. The mechanisms whereby aging reduces resiliency are poorly understood. Hedgehog is a signaling pathway with critical mitogenic and morphogenic functions during development. Recent studies indicate that Hedgehog regulates metabolic homeostasis in adult liver. The present study evaluates the hypothesis that Hedgehog signaling becomes dysregulated in hepatocytes during aging, resulting in decreased resiliency and therefore, impaired regeneration and enhanced vulnerability to damage. Partial hepatectomy (PH) was performed on young and old wild‐type mice and Smoothened (Smo)‐floxed mice treated with viral vectors to conditionally delete Smo and disrupt Hedgehog signaling specifically in hepatocytes. Changes in signaling were correlated with changes in regenerative responses and compared among groups. Old livers had fewer hepatocytes proliferating after PH. RNA sequencing identified Hedgehog as a top downregulated pathway in old hepatocytes before and after the regenerative challenge. Deleting Smo in young hepatocytes before PH prevented Hedgehog pathway activation after PH and inhibited regeneration. Gene Ontogeny analysis demonstrated that both old and Smo‐deleted young hepatocytes had activation of pathways involved in innate immune responses and suppression of several signaling pathways that control liver growth and metabolism. Hedgehog inhibition promoted telomere shortening and mitochondrial dysfunction in hepatocytes, consequences of aging that promote inflammation and impair tissue growth and metabolic homeostasis. Hedgehog signaling is dysregulated in old hepatocytes. This accelerates aging, resulting in decreased resiliency and therefore, impaired liver regeneration and enhanced vulnerability to damage.

Gadd45 in Senescence

Gadd45a, Gadd45b, and Gadd45g have been implicated in cell cycle arrest, DNA repair, apoptosis, innate immunity, genomic stability, and more recently in senescence. Evidence has accumulated that Gadd45a deficiency results in escape of mouse embryo fibroblasts from senescence, whereas Gadd45b deficiency promotes premature senescence and skin aging. Moreover, recently Gadd45b deficiency was found to promote senescence and attenuate liver fibrosis, whereas Gadd45a was observed to exert a protective effect against hepatic fibrosis. These findings indicate that the Gadd45 stress response proteins play important roles in modulating cellular responses to senescence. Thus, exploring how Gadd45 proteins modulate cellular senescence has the potential to provide new and innovative tools to treat cancer as well as liver disease.

Genetic and Cellular Contributions to Liver Regeneration

The regenerative capabilities of the liver represent a paradigm for understanding tissue repair in solid organs. Regeneration after partial hepatectomy in rodent models is well understood, while regeneration in the context of clinically relevant chronic injuries is less studied. Given the growing incidence of fatty liver disease, cirrhosis, and liver cancer, interest in liver regeneration is increasing. Here, we will review the principles, genetics, and cell biology underlying liver regeneration, as well as new approaches being used to study heterogeneity in liver tissue maintenance and repair.

PinX1 Depletion Improves Liver Injury in a Mouse Model of Nonalcoholic Fatty Liver Disease via Increasing Telomerase Activity and Inhibiting Apoptosis

PIN2/TRF1-interacting telomerase inhibitor 1 (PinX1) can inhibit tumor growth by inhibiting telomerase activity. However, only few studies investigated the expression and function of PinX1 in nonalcoholic fatty liver disease (NAFLD). Thus, here we aimed to explore the roles of PinX1 in high-fat diet (HFD)-induced NAFLD in mice and in isolated hepatocytes. The mRNA expression of PinX1 and mTERT as well as telomere length were analyzed by RT-PCR. Pathological changes were detected by HE staining and oil red O staining. Triglyceride, cholesterol, alanine aminotransferase, aspartic aminotransferase, and telomerase activity were detected by ELISA. Hepatocyte apoptosis was determined by TUNEL and flow cytometry, and protein expression was analyzed by western blotting. We found that the expression of PinX1 was upregulated in the HFD group compared with the WT group. PinX1 knockout improved HFD-induced liver injury in mice and exhibited less lipid accumulation in hepatocytes. Moreover, telomere length, telomerase activity, and mTERT expression were significantly reduced in liver tissues of HFD-induced mice and palmitic acid-induced hepatocytes, while PinX1 knockout attenuated the effect. Furthermore, HFD-induced PinX1-/- mice exhibited less hepatocyte apoptosis than HFD-induced WT mice. Besides, PinX1 knockout inhibited the increase of cleaved caspase-3 and cleaved PARP expression in vivo and in vitro. Moreover, inhibition of mTERT reversed the effect of PinX1 knockout in hepatocytes. Taken together, our findings indicate that PinX1 promotes hepatocyte apoptosis and lipid accumulation by decreasing telomere length and telomerase activity in the development of NAFLD. PinX1 might be a target for the treatment of NAFLD.

Cellular senescence in liver fibrosis: Implications for age-related chronic liver diseases

INTRODUCTION

New insights indicate a causative link between cellular senescence and liver fibrosis. Senescent hepatic stellate cells (HSCs) facilitate fibrosis resolution, while senescence in hepatocytes and cholangiocytes acts as a potent mechanism driving liver fibrogenesis. In many clinical studies, telomeres and mitochondrial DNA contents, which are both aging biomarkers, were reportedly associated with a degree of liver fibrosis in patients with chronic liver diseases (CLDs); this highlights their potential as biomarkers for liver fibrogenesis. A deeper understanding of mechanisms underlying multi-step progression of senescence may yield new therapeutic strategies for age-related chronic liver pathologies.

AREAS COVERED

This review examines the recent findings from preclinical and clinical studies on mechanisms of senescence in liver fibrogenesis and its involvement in liver fibrosis. A comprehensive literature search in electronic databases consisting of PubMed and Scopus from inception to 31 August 2021 was performed.

EXPERT OPINION

Cellular senescence has diagnostic, prognostic, and therapeutic potential in progressive liver complications, especially liver fibrosis. Stimulating or reinforcing the immune response against senescent cells may be a promising and forthright biotherapeutic strategy. This approach will need a deeper understanding of the immune system's ability to eliminate senescent cells and the molecular and cellular mechanisms underlying this process.

Differential Effectiveness of Tenofovir and Entecavir for Prophylaxis of Hepatocellular Carcinoma in Chronic Hepatitis B Patients Depending on Coexisting Cirrhosis and Prior Exposure to Antiviral Therapy: A Systematic Review and Meta-analysis

GOALS

This meta-analysis evaluated the comparative effectiveness of tenofovir disoproxil fumarate (TDF) versus entecavir (ETV) in reducing the risk of hepatocellular carcinoma (HCC).

BACKGROUND

It is unclear whether TDF or ETV is more effective in reducing the risk of HCC in chronic hepatitis B (CHB) patients with or without underlying cirrhosis.

METHODS

We searched the MEDLINE database through April 13, 2020, for studies involving CHB treated with TDF and/or ETV. Primary and secondary outcomes were the incidence of HCC and overall survival, respectively, calculated as risk ratios (RRs). Adjusted results were further evaluated by pooling propensity score matched cohorts.

RESULTS

Of the 229 records identified, 17 studies were included in the quantitative analysis. TDF treatment was associated with a significantly lower risk of HCC development [RR, 0.63; 95% confidence interval (CI), 0.43-0.93; P=0.024] and mortality (RR, 0.69; 95% CI, 0.57-0.84; P=0.003) than ETV treatment. Moreover, TDF significantly lowered HCC risk in patients with cirrhosis (RR, 0.69; 95% CI, 0.56-0.84) and antiviral treatment-naive patients (RR, 0.59; 95% CI, 0.35-0.98) compared with ETV. Among treatment-naive patients, TDF significantly prolonged survival compared with ETV (RR, 0.69; 95% CI, 0.52-0.91).

CONCLUSIONS

TDF likely confers a lower risk of HCC development and longer survival in patients with CHB, especially among treatment-naive patients and those with underlying cirrhosis, than ETV.

Transient elastography in adult patients with cryptic dyskeratosis congenita reveals subclinical liver fibrosis: a retrospective analysis of the Aachen telomere biology disease registry

Background

Telomere biology disorders (TBD) such as dyskeratosis congenita (DKC) lead to progressive multi-organ failure as impaired telomere maintenance disturbs cellular proliferative capacity. A wide range of hepatic manifestations from asymptomatic liver enzyme elevation to overt liver fibrosis/cirrhosis can be observed in TBD patients. However, the incidence of hepatic involvement remains unknown. Non-invasive transient elastography (TE) predicts early fibrosis by measuring liver stiffness and may uncover subclinical liver damage in TBD patients.

Methods

Liver screening procedures of nine TBD patients from the Aachen TBD Registry are being presented retrospectively. Following clinical suspicion, TBD was diagnosed using flow-FISH with telomere length (TL) below the 1% percentile and confirmed by next-generation sequencing (NGS) detecting pathogenic mutations in telomere maintenance genes TERC or TERT.

Results

In all patients, TBD was first diagnosed in adulthood. Patients showed normal to slightly elevated liver function test parameters. Hepatic ultrasound revealed inhomogeneous parenchyma in seven (77.7%) and increased liver echogenicity in four patients (44.4%). Median liver stiffness was 10.7 kilopascal (kPa) (interquartile range 8.4, 15.7 kPa). Using 7.1 kPa as cut-off, 88.8% of patients were classified as moderate fibrosis to cirrhosis.

Conclusion

Subclinical chronic liver involvement is frequent in patients with adult-onset TBD. TE could have a valuable role in the routine work-up of patients with telomere disorders including DKC for early detection of patients at risk for liver function impairment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-02024-8.

Senescence in HBV-, HCV- and NAFLD- Mediated Hepatocellular Carcinoma and Senotherapeutics: Current Evidence and Future Perspective

Cell senescence constitutes a physiological process that serves as protection from malignant transformation of cells. However, recent scientific discoveries also identify cell senescence as pivotal in hepatocellular cancer (HCC) biology. The review herein aimed to accumulate evidence on senescence as a mediator of HCC occurrence in hepatitis B (HBV), C (HCV) virus infections, and non-alcoholic fatty liver disease (NAFLD). In HBV infection, the carcinogenic HBV X protein frequently mutates during chronic infection, and subsequently exhibits different effects on senescence. In HCV infection, senescent non-functional T-cells do not effectively clear pre-malignant hepatocytes. Furthermore, the HCV Core protein inhibits the occurrence of normal stress-induced hepatocyte senescence, allowing damaged cells to maintain their proliferative potential. In NAFLD-mediated HCC, current data point towards the gut microbiome and hepatic stellate cell senescence. Additionally, senescence contributes in the development of resistance in targeted therapies, such as sorafenib. Finally, the promising role of senotherapeutics in HCC was also explored. Overall, although we may still be at a primitive stage in fully unraveling the role of senescence in cancer, it seems that understanding and harnessing senescence may have the potential to revolutionize the way we treat hepatocellular cancer.

Association between telomere length and hepatic fibrosis in non-alcoholic fatty liver disease

Telomere length has been linked to the prevalence and progression of metabolic disease. However, clinical implications of telomere length in biopsy-proven non-alcoholic fatty liver disease (NAFLD) patients remain unclear. Therefore, this study aimed to investigate the association of telomere length with the histological severity of NAFLD. The cross-sectional data derived from the prospectively enrolled Boramae NAFLD registry (n = 91) were analyzed. The liver tissues and clinical information were obtained from both NAFLD patients and non-NAFLD subjects. Binary logistic regression was performed to identify the independent association between telomere length and the histological severity of NAFLD. A total of 83 subjects with or without biopsy-proven NAFLD were included for analysis: non-NAFLD in 23 (27.7%), non-alcoholic fatty liver in 15 (18.1%), and non-alcoholic steatohepatitis (NASH) in 45 (54.2%). Telomere length measured from liver tissues showed a strong negative correlation (p < 0.001) with age, regardless of NAFLD status. Therefore, telomere length was corrected for age. Age-adjusted telomere length than decreased gradually with an increasing severity of fibrosis in patients with NAFLD (p < 0.028). In multivariate analysis, age-adjusted telomere length (odds ratio [OR] 0.59; 95% CI 0.37–0.92; p = 0.019) and high-density lipoprotein cholesterol (OR 0.94; 95% CI 0.80–0.99; p = 0.039) were independently associated with significant fibrosis. The age-adjusted telomere length tends to decrease along with the fibrosis stage of NAFLD. In particular, among the histological components of NAFLD, fibrosis severity seems to be related to telomere length in the liver.

Fibroageing: An ageing pathological feature driven by dysregulated extracellular matrix-cell mechanobiology

Ageing is a multifactorial biological process leading to a progressive decline of physiological functions. The process of ageing includes numerous changes in the cells and the interactions between cell-cell and cell-microenvironment remaining as a critical risk factor for the development of chronic degenerative diseases. Systemic inflammation, known as inflammageing, increases as a consequence of ageing contributing to age-related morbidities. But also, persistent and uncontrolled activation of fibrotic pathways, with excessive accumulation of extracellular matrix (ECM) and organ dysfunction is markedly more frequent in the elderly. In this context, we introduce here the concept of Fibroageing, that is, the propensity to develop tissue fibrosis associated with ageing, and propose that ECM is a key player underlying this process. During ageing, molecules of the ECM become damaged through many modifications including glycation, crosslinking, and accumulation, leading to matrix stiffness which intensifies ageing-associated alterations. We provide a framework with some mechanistic hypotheses proposing that stiff ECM, in addition to the well-known activation of fibrotic positive feedback loops, affect several of the hallmarks of ageing, such as cell senescence and mitochondrial dysfunction, and in this context, is a key mechanism and a driver thread of Fibroageing.

Inverse Association of Telomere Length With Liver Disease and Mortality in the US Population

Physiologic aging leads to attrition of telomeres and replicative senescence. An acceleration of this process has been hypothesized in the progression of chronic liver disease. We sought to examine the association of telomere length (TL) with liver disease and its impact on mortality risk. A cohort of 7,072 adults with leukocyte TL measurements from the National Health and Nutrition Examination Survey 1999‐2002 with mortality follow‐up through 2015 was analyzed. Liver disease was defined by aminotransferase levels and classified into etiology‐based and advanced fibrosis categories. Multivariable‐adjusted linear regression models estimated effect sizes, with 95% confidence intervals (CIs), of the presence of liver disease on TL. Cox regression models evaluated associations between TL and all‐cause mortality risk using adjusted hazard ratios (HRs). The cohort was representative of the US population with mean age 46.1 years and mean TL 5.79 kilobase pairs. No overall association between TL and liver disease was found; however, there was a significant negative association of TL and advanced liver fibrosis in individuals aged 65 and above. The liver disease cohort (HR 1.22, 95% CI 0.99‐1.51) and those with metabolic syndrome (HR 1.26, 95% CI 0.96‐1.67) had increased mortality risk with shorter TL. The relationship between TL and all‐cause mortality was stronger in women (HR 1.51, 95% CI 1.02‐2.23) and in non‐Hispanic Whites (HR 1.37, 95% CI 1.02‐1.84). Conclusion: Shortened leukocyte TL is independently associated with advanced liver disease at older ages, and with a higher risk of all‐cause mortality in those with liver disease. These associations reaffirm the need to better understand the role of telomeres in the progression of liver disease.

Breathe it in - Spotlight on senescence and regeneration in the lung

Cellular senescence, a highly coordinated and programmed cellular state, has a functional role in both lung physiology and pathology. While the contribution of senescent cells is recognized in the context of ageing and age-related pulmonary diseases, relatively less is known how cellular senescence of functionally distinct cell types leads to the progression of these pathologies. Recent advances in tools to track and isolate senescent cells from tissues, shed a light on the identity, behavior and function of senescent cells in vivo. The transient presence of senescent cells has an indispensable role in limiting lung damage and contributes to organ regenerative capacity upon acute stress insults. In contrast, persistent accumulation of senescent cells is a driver of age-related decline in organ function. Here, we discuss lung physiology and pathology as an example of seemingly contradictory role of senescence in structural and functional integrity of the tissue upon damage, and in age-related pulmonary diseases.

Senescence in tissue samples of humans with age-related diseases: A systematic review

BACKGROUND

Higher numbers of senescent cells have been implicated in age-related disease pathologies. However, whether different diseases have different senescent phenotypes is unknown. Here we provide a systematic overview of the current available evidence of senescent cells in age-related diseases pathologies in humans and the markers currently used to detect senescence levels in humans.

METHODS

PubMed, Web of Science and EMBASE were systematically searched from inception to the 29^th of September 2019, using keywords related to 'senescence', 'age-related diseases' and 'biopsies'.

RESULTS

In total 12,590 articles were retrieved of which 103 articles were included in this review. The role of senescence in age-related disease has been assessed in 9 different human organ system and 27 different age-related diseases of which heart (27/103) and the respiratory systems (18/103) are the most investigated. Overall, 27 different markers of senescence have been used to determine cellular senescence and the cell cycle regulator p16^ink4a is most often used (23/27 age-related pathologies).

CONCLUSION

This review demonstrates that a higher expression of senescence markers are observed within disease pathologies. However, not all markers to detect senescence have been assessed in all tissue types.

Impact of Aging on Liver Cells and Liver Disease: Focus on the Biliary and Vascular Compartments

The aging process is represented by the time-dependent decay in physiologic functions of living beings. Major interest has been focused in recent years on the determinants of this progressive condition due to its correlative relationship with the onset of diseases. Several hallmark features have been observed in aging, such as genetic alterations, mitochondrial impairment, and telomere shortening. At the cellular level, a senescent phenotype has been identified in response to aging that is characterized by a flat appearance, proliferative arrest, and production of specific molecules. The net effect of these cells in the course of diseases is an argument of debate. In fact, while the onset of a senescent phenotype may prevent tumor spreading, these cells appear to support pathological processes in some conditions. Several studies are now focused on clarifying the specific molecular pathways of aging/senescence in different cells, tissues, or organs. Biliary and vascular components, within the liver, have emerged as important determinants of some form of liver disease. In this review we summarize the most recent achievements on aging/senescence, focusing on the biliary and vascular liver system. Conclusion: Several findings, in both preclinical animal models and on human liver specimens, converge in supporting the presence of specific aging hallmarks in the diseases involving these hepatic compartments.

When dormancy fuels tumour relapse

Tumour recurrence is a serious impediment to cancer treatment, but the mechanisms involved are poorly understood. The most frequently used anti-tumour therapies-chemotherapy and radiotherapy-target highly proliferative cancer cells. However non- or slow-proliferative dormant cancer cells can persist after treatment, eventually causing tumour relapse. Whereas the reversible growth arrest mechanism allows quiescent cells to re-enter the cell cycle, senescent cells are largely thought to be irreversibly arrested, and may instead contribute to tumour growth and relapse through paracrine signalling mechanisms. Thus, due to the differences in their growth arrest mechanism, metabolic features, plasticity and adaptation to their respective tumour microenvironment, dormant-senescent and -quiescent cancer cells could have different but complementary roles in fuelling tumour growth. In this review article, we discuss the implication of dormant cancer cells in tumour relapse and the need to understand how quiescent and senescent cells, respectively, may play a part in this process.

Onset of Senescence and Steatosis in Hepatocytes as a Consequence of a Shift in the Diacylglycerol/Ceramide Balance at the Plasma Membrane

Ceramide and diacylglycerol (DAG) are bioactive lipids and mediate many cellular signaling pathways. Sphingomyelin synthase (SMS) is the single metabolic link between the two, while SMS2 is the only SMS form located at the plasma membrane. SMS2 functions were investigated in HepG2 cell lines stably expressing SMS2. SMS2 overexpression did not alter sphingomyelin (SM), phosphatidylcholine (PC), or ceramide levels. DAG content increased by approx. 40% and led to downregulation of DAG-dependent protein kinase C (PKC). SMS2 overexpression also induced senescence, characterized by positivity for β-galactosidase activity and heterochromatin foci. HepG2-SMS2 cells exhibited protruded mitochondria and suppressed mitochondrial respiration rates. ATP production and the abundance of Complex V were substantially lower in HepG2-SMS2 cells as compared to controls. SMS2 overexpression was associated with inflammasome activation based on increases in IL-1β and nlpr3 mRNA levels. HepG2-SMS2 cells exhibited lipid droplet accumulation, constitutive activation of AMPK based on elevated ¹⁷²Thr phosphorylation, increased AMPK abundance, and insensitivity to insulin suppression of AMPK. Thus, our results show that SMS2 regulates DAG homeostasis and signaling in hepatocytes and also provide proof of principle for the concept that offset in bioactive lipids’ production at the plasma membrane can drive the senescence program in association with steatosis and, seemingly, by cell-autonomous mechanisms.

Could protein content of Urinary Extracellular Vesicles be useful to detect Cirrhosis in Alcoholic Liver Disease?

Alcohol abuse has a high impact on the mortality and morbidity related to a great number of diseases and is responsible for the development of alcoholic liver disease (ALD). It remains challenging to detect and evaluate its severity, which is crucial for prognosis. In this work, we studied if urinary EVs (uEVs) could serve in diagnose and evaluate cirrhosis in ALD. To this purpose, uEVs characterization by cryo-electron microscopy (Cryo-EM), Nanoparticle Tracking Analysis (NTA) and Western blotting (WB) was performed in a cohort of 21 controls and 21 cirrhotic patients. Then, proteomics of uEVs was carried out in a second cohort of 6 controls and 8 patients in order to identify new putative biomarkers for cirrhosis in ALD. Interestingly, uEVs concentration, size and protein composition were altered in cirrhotic patients. From a total of 1304 proteins identified in uEVs, 90 of them were found to be altered in cirrhotic patients. The results suggest that uEVs could be considered as a tool and a supplier of new biomarkers for cirrhosis in ALD, whose application would be especially relevant in chronic patients. Yet, further research is necessary to obtain more relevant result in clinical terms.

Evaluating causality of cellular senescence in non-alcoholic fatty liver disease

Cellular senescence is a state of irreversible cell cycle arrest that has important physiological functions. However, cellular senescence is also a hallmark of ageing and has been associated with several pathological conditions. A wide range of factors including genotoxic stress, mitogens and inflammatory cytokines can induce senescence. Phenotypically, senescent cells are characterised by short telomeres, an enlarged nuclear area and damaged genomic and mitochondrial DNA. Secretion of proinflammatory proteins, also known as the senescence-associated secretory phenotype, is a characteristic of senescent cells that is thought to be the main contributor to their disease-inducing properties. In the past decade, the role of cellular senescence in the development of non-alcoholic fatty liver disease (NAFLD) and its progression towards non-alcoholic steatohepatitis (NASH) has garnered significant interest. Until recently, it was suggested that hepatocyte cellular senescence is a mere consequence of the metabolic dysregulation and inflammatory phenomena in fatty liver disease. However, recent work in rodents has suggested that senescence may be a causal factor in NAFLD development. Although causality is yet to be established in humans, current evidence suggests that targeting senescent cells has therapeutic potential for NAFLD. We aim to provide insights into the quality of the evidence supporting a causal role of cellular senescence in the development of NAFLD in rodents and humans. We will elaborate on key cellular and molecular features of senescence and discuss the efficacy and safety of novel senolytic drugs for the treatment or prevention of NAFLD.

Telomere length is key to hepatocellular carcinoma diversity and telomerase addiction is an actionable therapeutic target

BACKGROUND & AIMS

Telomerase activation is the earliest event in hepatocellular carcinoma (HCC) development. Thus, we aimed to elucidate the role of telomere length maintenance during liver carcinogenesis.

METHODS

Telomere length was measured in the tumor and non-tumor liver tissues of 1,502 patients (978 with HCC) and integrated with TERT alterations and expression, as well as clinical and molecular (analyzed by genome, exome, targeted and/or RNA-sequencing) features of HCC. The preclinical efficacy of anti-TERT antisense oligonucleotides (ASO) was assessed in vitro in 26 cell lines and in vivo in a xenograft mouse model.

RESULTS

Aging, liver fibrosis, male sex and excessive alcohol consumption were independent determinants of liver telomere attrition. HCC that developed in livers with long telomeres frequently had wild-type TERT with progenitor features and BAP1 mutations. In contrast, HCC that developed on livers with short telomeres were enriched in the non-proliferative HCC class and frequently had somatic TERT promoter mutations. In HCCs, telomere length is stabilized in a narrow biological range around 5.7 kb, similar to non-tumor livers, by various mechanisms that activate TERT expression. Long telomeres are characteristic of very aggressive HCCs, associated with the G3 transcriptomic subclass, TP53 alterations and poor prognosis. In HCC cell lines, TERT silencing with ASO was efficient in highly proliferative and poorly differentiated cells. Treatment for 3 to 16 weeks induced cell proliferation arrest in 12 cell lines through telomere shortening, DNA damage and activation of apoptosis. The therapeutic effect was also obtained in a xenograft mouse model.

CONCLUSIONS

Telomere maintenance in HCC carcinogenesis is diverse, and is associated with tumor progression and aggressiveness. The efficacy of anti-TERT ASO treatment in cell lines revealed the oncogenic addiction to TERT in HCC, providing a preclinical rationale for anti-TERT ASO treatment in HCC clinical trials.

LAY SUMMARY

Telomeres are repeated DNA sequences that protect chromosomes and naturally shorten in most adult cells because of the inactivation of the TERT gene, coding for the telomerase enzyme. Here we show that telomere attrition in the liver, modulated by aging, sex, fibrosis and alcohol, associates with specific clinical and molecular features of hepatocellular carcinoma, the most frequent primary liver cancer. We also show that liver cancer is dependent on TERT reactivation and telomere maintenance, which could be targeted through a novel therapeutic approach called antisense oligonucleotides.

Molecular mapping of interstitial lung disease reveals a phenotypically distinct senescent basal epithelial cell population

Compromised regenerative capacity of lung epithelial cells can lead to cellular senescence, which may precipitate fibrosis. While increased markers of senescence have been reported in idiopathic pulmonary fibrosis (IPF), the origin and identity of these senescent cells remain unclear, and tools to characterize context-specific cellular senescence in human lung are lacking. We observed that the senescent marker p16 is predominantly localized to bronchiolized epithelial structures in scarred regions of IPF and systemic sclerosis-associated interstitial lung disease (SSc-ILD) lung tissue, overlapping with the basal epithelial markers Keratin 5 and Keratin 17. Using in vitro models, we derived transcriptional signatures of senescence programming specific to different types of lung epithelial cells and interrogated these signatures in a single-cell RNA-Seq data set derived from control, IPF, and SSc-ILD lung tissue. We identified a population of basal epithelial cells defined by, and enriched for, markers of cellular senescence and identified candidate markers specific to senescent basal epithelial cells in ILD that can enable future functional studies. Notably, gene expression of these cells significantly overlaps with terminally differentiating cells in stratified epithelia, where it is driven by p53 activation as part of the senescence program.

Decreased expression of TERT and telomeric proteins as human ovaries age may cause telomere shortening

OBJECTIVE

Telomeres are repetitive sequences localized at the ends of eukaryotic chromosomes comprising noncoding DNA and telomere-binding proteins. TRF1 and TRF2 both bind to the double-stranded telomeric DNA to regulate its length throughout the lifespan of eukaryotic cells. POT1 interacts with single-stranded telomeric DNA and contributes to protecting genomic integrity. Previous studies have shown that telomeres gradually shorten as ovaries age, coinciding with fertility loss. However, the molecular background of telomere shortening with ovarian aging is not fully understood.

METHODS

The present study aimed to determine the spatial and temporal expression levels of the TERT, TRF1, TRF2, and POT1 proteins in different groups of human ovaries: fetal (n = 11), early postnatal (n = 10), premenopausal (n = 12), and postmenopausal (n = 14). Also, the relative telomere signal intensity of each group was measured using the Q-FISH method.

RESULTS

We found that the telomere signal intensities decreased evenly and significantly from fetal to postmenopausal groups (P < 0.05). The TERT, TRF1, TRF2, and POT1 proteins were localized in the cytoplasmic and nuclear regions of the oocytes, granulosa and stromal cells. Furthermore, the expression levels of these proteins reduced significantly from fetal to postmenopausal groups (P < 0.05).

CONCLUSION

These findings suggest that decreased TERT and telomere-binding protein expression may underlie the telomere shortening of ovaries with age, which may be associated with female fertility loss. Further investigations are required to elicit the molecular mechanisms regulating the gradual decrease in the expression of TERT and telomere-binding proteins in human oocytes and granulosa cells during ovarian aging.

Long-term risk of primary liver cancers in entecavir versus tenofovir treatment for chronic hepatitis B

It remains controversial whether entecavir (ETV) and tenofovir disoproxil fumarate (TDF) is associated with different clinical outcomes for chronic hepatitis B (CHB). This study aimed to compare the long-term risk of ETV versus TDF on hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC) in CHB patients from a large multi-institutional database in Taiwan. From 2011 to 2018, a total of 21,222 CHB patients receiving ETV or TDF were screened for eligibility. Patients with coinfection, preexisting cancer and less than 6 months of follow-up were excluded. Finally, 7248 patients (5348 and 1900 in the ETV and TDF groups, respectively) were linked to the National Cancer Registry database for the development of HCC or ICC. Propensity score matching (PSM) (2:1) analysis was used to adjust for baseline differences. The HCC incidence between two groups was not different in the entire population (hazard ratio [HR] 0.82; 95% confidence interval [CI] 0.66–1.02, p = 0.078) and in the PSM population (HR 0.83; 95% CI 0.65–1.06, p = 0.129). Among decompensated cirrhotic patients, a lower risk of HCC was observed in TDF group than in ETV group (HR 0.54; 95% CI 0.30–0.98, p = 0.043, PSM model). There were no differences between ETV and TDF groups in the ICC incidence (HR 1.84; 95% CI 0.54–6.29, p = 0.330 in the entire population and HR 1.04; 95% CI 0.31–3.52, p = 0.954 in the PSM population, respectively). In conclusion, treatment with ETV and TDF showed a comparable long-term risk of HCC and ICC in CHB patients.

Telomeres: history, health, and hallmarks of aging

The escalating social and economic burden of an aging world population has placed aging research at center stage. The hallmarks of aging comprise diverse molecular mechanisms and cellular systems that are interrelated and act in concert to drive the aging process. Here, through the lens of telomere biology, we examine how telomere dysfunction may amplify or drive molecular biological processes underlying each hallmark of aging and contribute to development of age-related diseases such as neurodegeneration and cancer. The intimate link of telomeres to aging hallmarks informs preventive and therapeutic interventions designed to attenuate aging itself and reduce the incidence of age-associated diseases.

Cellular Senescence in Liver Disease and Regeneration

Cellular senescence is an irreversible cell cycle arrest implemented by the cell as a result of stressful insults. Characterized by phenotypic alterations, including secretome changes and genomic instability, senescence is capable of exerting both detrimental and beneficial processes. Accumulating evidence has shown that cellular senescence plays a relevant role in the occurrence and development of liver disease, as a mechanism to contain damage and promote regeneration, but also characterizing the onset and correlating with the extent of damage. The evidence of senescent mechanisms acting on the cell populations of the liver will be described including the role of markers to detect cellular senescence. Overall, this review intends to summarize the role of senescence in liver homeostasis, injury, disease, and regeneration.

Remodeling of whole-body lipid metabolism and a diabetic-like phenotype caused by loss of CDK1 and hepatocyte division

Cell cycle progression and lipid metabolism are well-coordinated processes required for proper cell proliferation. In liver diseases that arise from dysregulated lipid metabolism, hepatocyte proliferation is diminished. To study the outcome of CDK1 loss and blocked hepatocyte proliferation on lipid metabolism and the consequent impact on whole-body physiology, we performed lipidomics, metabolomics, and RNA-seq analyses on a mouse model. We observed reduced triacylglycerides in liver of young mice, caused by oxidative stress that activated FOXO1 to promote the expression of Pnpla2/ATGL. Additionally, we discovered that hepatocytes displayed malfunctioning β-oxidation, reflected by increased acylcarnitines (ACs) and reduced β-hydroxybutyrate. This led to elevated plasma free fatty acids (FFAs), which were transported to the adipose tissue for storage and triggered greater insulin secretion. Upon aging, chronic hyperinsulinemia resulted in insulin resistance and hepatic steatosis through activation of LXR. Here, we demonstrate that loss of hepatocyte proliferation is not only an outcome but also possibly a causative factor for liver pathology.

Senescence in RASopathies, a possible novel contributor to a complex pathophenoype

Senescence is a biological process that induces a permanent cell cycle arrest and a specific gene expression program in response to various stressors. Following studies over the last few decades, the concept of senescence has evolved from an antiproliferative mechanism in cancer (oncogene-induced senescence) to a critical component of physiological processes associated with embryonic development, tissue regeneration, ageing and its associated diseases. In somatic cells, oncogenic mutations in RAS-MAPK pathway genes are associated with oncogene-induced senescence and cancer, while germline mutations in the same pathway are linked to a group of monogenic developmental disorders generally termed RASopathies. Here, we consider that in these disorders, senescence induction may result in opposing outcomes, a tumour protective effect and a possible contributor to a premature ageing phenotype identified in Costello syndrome, which belongs to the RASopathy group. In this review, we will highlight the role of senescence in organismal homeostasis and we will describe the current knowledge about senescence in RASopathies. Additionally, we provide a perspective on examples of experimentally characterised RASopathy mutations that, alone or in combination with various stressors, may also trigger an age-dependent chronic senescence, possibly contributing to the age-dependent worsening of RASopathy pathophenotype and the reduction of lifespan.

The role of senescent T cells in immunopathology

The development of senescence in tissues of different organs and in the immune system are usually investigated independently of each other although during ageing, senescence in both cellular systems develop concurrently. Senescent T cells are highly inflammatory and secrete cytotoxic mediators and express natural killer cells receptors (NKR) that bypass their antigen specificity. Instead they recognize stress ligands that are induced by inflammation or infection of different cell types in tissues. In this article we discuss data on T cell senescence, how it is regulated and evidence for novel functional attributes of senescent T cells. We discuss an interactive loop between senescent T cells and senescent non-lymphoid cells and conclude that in situations of intense inflammation, senescent cells may damage healthy tissue. While the example for immunopathology induced by senescent cells that we highlight is cutaneous leishmaniasis, this situation of organ damage may apply to other infections, including COVID-19 and also rheumatoid arthritis, where ageing, inflammation and senescent cells are all part of the same equation.

Molecular Mechanisms to Target Cellular Senescence in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) has emerged as a major cause of cancer-related death and is the most common type of liver cancer. Due to the current paucity of drugs for HCC therapy there is a pressing need to develop new therapeutic concepts. In recent years, the role of Serum Response Factor (SRF) and its coactivators, Myocardin-Related Transcription Factors A and B (MRTF-A and -B), in HCC formation and progression has received considerable attention. Targeting MRTFs results in HCC growth arrest provoked by oncogene-induced senescence. The induction of senescence acts as a tumor-suppressive mechanism and therefore gains consideration for pharmacological interventions in cancer therapy. In this article, we describe the key features and the functional role of senescence in light of the development of novel drug targets for HCC therapy with a focus on MRTFs.

Immunomodulatory Role of the Extracellular Matrix Within the Liver Disease Microenvironment

Chronic liver disease when accompanied by underlying fibrosis, is characterized by an accumulation of extracellular matrix (ECM) proteins and chronic inflammation. Although traditionally considered as a passive and largely architectural structure, the ECM is now being recognized as a source of potent damage-associated molecular pattern (DAMP)s with immune-active peptides and domains. In parallel, the ECM anchors a range of cytokines, chemokines and growth factors, all of which are capable of modulating immune responses. A growing body of evidence shows that ECM proteins themselves are capable of modulating immunity either directly via ligation with immune cell receptors including integrins and TLRs, or indirectly through release of immunoactive molecules such as cytokines which are stored within the ECM structure. Notably, ECM deposition and remodeling during injury and fibrosis can result in release or formation of ECM-DAMPs within the tissue, which can promote local inflammatory immune response and chemotactic immune cell recruitment and inflammation. It is well described that the ECM and immune response are interlinked and mutually participate in driving fibrosis, although their precise interactions in the context of chronic liver disease are poorly understood. This review aims to describe the known pro-/anti-inflammatory and fibrogenic properties of ECM proteins and DAMPs, with particular reference to the immunomodulatory properties of the ECM in the context of chronic liver disease. Finally, we discuss the importance of developing novel biotechnological platforms based on decellularized ECM-scaffolds, which provide opportunities to directly explore liver ECM-immune cell interactions in greater detail.

Loss of hepatocyte cell division leads to liver inflammation and fibrosis

The liver possesses a remarkable regenerative capacity based partly on the ability of hepatocytes to re-enter the cell cycle and divide to replace damaged cells. This capability is substantially reduced upon chronic damage, but it is not clear if this is a cause or consequence of liver disease. Here, we investigate whether blocking hepatocyte division using two different mouse models affects physiology as well as clinical liver manifestations like fibrosis and inflammation. We find that in P14 Cdk1Liv-/- mice, where the division of hepatocytes is abolished, polyploidy, DNA damage, and increased p53 signaling are prevalent. Cdk1Liv-/- mice display classical markers of liver damage two weeks after birth, including elevated ALT, ALP, and bilirubin levels, despite the lack of exogenous liver injury. Inflammation was further studied using cytokine arrays, unveiling elevated levels of CCL2, TIMP1, CXCL10, and IL1-Rn in Cdk1Liv-/- liver, which resulted in increased numbers of monocytes. Ablation of CDK2-dependent DNA re-replication and polyploidy in Cdk1Liv-/- mice reversed most of these phenotypes. Overall, our data indicate that blocking hepatocyte division induces biological processes driving the onset of the disease phenotype. It suggests that the decrease in hepatocyte division observed in liver disease may not only be a consequence of fibrosis and inflammation, but also a pathological cue.

Short Telomeres: Cause and Consequence in Liver Disease

Short telomere syndrome is a genetically inherited syndrome resulting in premature telomere shortening. This premature shortening of telomeres can result in hematologic, pulmonary, vascular, gastrointestinal, and hepatic manifestations of disease. Identifying patients with short telomere syndrome can be a clinical challenge due to the multitude of potential manifestations and lack of widely available diagnostic tests. In this review, we will highlight hepatic manifestations of short telomere syndrome with a focus on diagnosis, testing, and potential treatments.

Cell Therapy for Liver Disease: From Promise to Reality

Over the last decade, there has been a considerable progress in the development of cell therapy products for the treatment of liver diseases. The quest to generate well-defined homogenous cell populations with defined mechanism(s) of action has enabled the progression from use of autologous bone marrow stem cells comprising of heterogeneous cell populations to allogeneic cell types such as monocyte-derived macrophages, regulatory T cells, mesenchymal stromal cells, macrophages, etc. There is growing evidence regarding the multiple molecular mechanisms pivotal to various therapeutic effects and hence, careful selection of cell therapy product for the desired putative effects is crucial. In this review, we have presented an overview of the cell therapies that have been developed thus far, with preclinical and clinical evidence for their use in liver disease. Limitations associated with these therapies have also been discussed. Despite the advances made, there remain multiple challenges to overcome before cell therapies can be considered as viable treatment options, and these include larger scale clinical trials, scalable production of cells according to good manufacturing practice standards, pathways for delivery of cell therapy within hospital environments, and costs associated with the production.

Telomere Dysfunction Activates p53 and Represses HNF4α Expression Leading to Impaired Human Hepatocyte Development and Function

BACKGROUND AND AIMS

Telomere attrition is a major risk factor for end-stage liver disease. Due to a lack of adequate models and intrinsic difficulties in studying telomerase in physiologically relevant cells, the molecular mechanisms responsible for liver disease in patients with telomere syndromes remain elusive. To circumvent that, we used genome editing to generate isogenic human embryonic stem cells (hESCs) harboring clinically relevant mutations in telomerase and subjected them to an in vitro, stage-specific hepatocyte differentiation protocol that resembles hepatocyte development in vivo.

APPROACH AND RESULTS

Using this platform, we observed that while telomerase is highly expressed in hESCs, it is quickly silenced, specifically due to telomerase reverse transcriptase component (TERT) down-regulation, immediately after endoderm differentiation and completely absent in in vitro-derived hepatocytes, similar to what is observed in human primary hepatocytes. While endoderm derivation is not impacted by telomere shortening, progressive telomere dysfunction impaired hepatic endoderm formation. Consequently, hepatocyte derivation, as measured by expression of specific hepatic markers as well by albumin expression and secretion, is severely compromised in telomerase mutant cells with short telomeres. Interestingly, this phenotype was not caused by cell death induction or senescence. Rather, telomere shortening prevents the up-regulation and activation of human hepatocyte nuclear factor 4 alpha (HNF4α) in a p53-dependent manner. Both reactivation of telomerase and silencing of p53 rescued hepatocyte formation in telomerase mutants. Likewise, the conditional expression (doxycycline-controlled) of HNF4α, even in cells that retained short telomeres, accrued DNA damage, and exhibited p53 stabilization, successfully restored hepatocyte formation from hESCS.

CONCLUSIONS

Our data show that telomere dysfunction acts as a major regulator of HNF4α during hepatocyte development, pointing to a target in the treatment of liver disease in telomere-syndrome patients.

Epithelial Plasticity during Liver Injury and Regeneration

Following injury, the liver's epithelial cells regenerate efficiently with rapid proliferation of hepatocytes and biliary cells. However, when proliferation of resident epithelial cells is impaired, alternative regeneration mechanisms can occur. Intricate lineage-tracing strategies and experimental models of regenerative stress have revealed a degree of plasticity between hepatocytes and biliary cells. New technologies such as single-cell omics, in combination with functional studies, will be instrumental to uncover the remaining unknowns in the field. In this review, we evaluate the experimental and clinical evidence for epithelial plasticity in the liver and how this influences the development of therapeutic strategies for chronic liver disease.

Single-cell technologies in hepatology: new insights into liver biology and disease pathogenesis

Liver disease is a major global health-care problem, affecting an estimated 844 million people worldwide. Despite this substantial burden, therapeutic options for liver disease remain limited, in part owing to a paucity of detailed analyses defining the cellular and molecular mechanisms that drive these conditions in humans. Single-cell transcriptomic technologies are transforming our understanding of cellular diversity and function in health and disease. In this Review, we discuss how these technologies have been applied in hepatology, advancing our understanding of cellular heterogeneity and providing novel insights into fundamental liver biology such as the metabolic zonation of hepatocytes, endothelial cells and hepatic stellate cells, and the cellular mechanisms underpinning liver regeneration. Application of these methodologies is also uncovering critical pathophysiological changes driving disease states such as hepatic fibrosis, where distinct populations of macrophages, endothelial cells and mesenchymal cells reside within a spatially distinct fibrotic niche and interact to promote scar formation. In addition, single-cell approaches are starting to dissect key cellular and molecular functions in liver cancer. In the near future, new techniques such as spatial transcriptomics and multiomic approaches will further deepen our understanding of disease pathogenesis, enabling the identification of novel therapeutic targets for patients across the spectrum of liver diseases.

Molecular Mechanisms Underlying Hepatocellular Carcinoma Induction by Aberrant NRF2 Activation-Mediated Transcription Networks: Interaction of NRF2-KEAP1 Controls the Fate of Hepatocarcinogenesis

NF-E2-related factor 2 (NRF2) is a basic leucine zipper transcription factor, a master regulator of redox homeostasis regulating a variety of genes for antioxidant and detoxification enzymes. NRF2 was, therefore, initially thought to protect the liver from oxidative stress. Recent studies, however, have revealed that mutations in NRF2 cause aberrant accumulation of NRF2 in the nucleus and exert the upregulation of NRF2 target genes. Moreover, among all molecular changes in hepatocellular carcinoma (HCC), NRF2 activation has been revealed as a more prominent pathway contributing to the progression of precancerous lesions to malignancy. Nevertheless, how its activation leads to poor prognosis in HCC patients remains unclear. In this review, we provide an overview of how aberrant activation of NRF2 triggers HCC development. We also summarize the emerging roles of other NRF family members in liver cancer development.

Telomere Length Increase in HIV/HCV-Coinfected Patients with Cirrhosis after HCV Eradication with Direct-Acting Antivirals

Introduction: Human immunodeficiency virus (HIV) infection and cirrhosis are associated with a senescent phenotype that decreases telomere length. We evaluated the impact of hepatitis C virus (HCV) elimination on telomere length in patients with advanced HCV-related cirrhosis after sustained virological response (SVR), with all-oral direct-acting antiviral agents (DAAs). Methods: Prospective study of 60 HIV/HCV-coinfected and 30 HCV-monoinfected patients with advanced HCV cirrhosis (liver decompensation or liver stiffness measurement (LSM) ≥ 25 kPa, hepatic liver pressure gradient (HVPG) ≥ 10 mmHg, or Child–Pugh–Turcotte (CPT) ≥ 7). The relative telomere length (RTL) was quantified by real-time multiplex PCR (MMqPCR) on peripheral blood mononuclear cells at baseline and 48 weeks after HCV treatment. Generalized linear models (GLMs) adjusted for the most relevant clinical and epidemiological variables and mixed GLMs were used. Results: In comparison with HCV-monoinfected patients, HIV/HCV-coinfected patients were younger (p < 0.001), had lower body mass index (BMI) (p = 0.002), and had been exposed less frequently to interferons (p = 0.011). In addition, they were more frequently men (p = 0.011), smokers (p = 0.005), prior intravenous drug users (IVDUs) (p < 0.001), and alcohol abusers (p = 0.005). RTL was significantly lower in HIV/HCV-coinfected patients than in HCV-monoinfected patients, both at baseline (p < 0.001), and at the end of follow-up (p = 0.032). A significant RTL increase over time was found only for HIV/HCV-coinfected patients (p < 0.001), especially in those patients with compensated cirrhosis (p < 0.001). Conclusion: HCV eradication with all-oral DAAs was associated with an increase in telomere length in HIV/HCV-coinfected patients with advanced cirrhosis, particularly in compensated patients. This finding suggests that HCV clearance may have implications in age-related conditions in this population group.

Telomeres and Telomerase in the Development of Liver Cancer

Liver cancer is one of the most common cancer types worldwide and the fourth leading cause of cancer-related death. Liver carcinoma is distinguished by a high heterogeneity in pathogenesis, histopathology and biological behavior. Dysregulated signaling pathways and various gene mutations are frequent in hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (iCCA), which represent the two most common types of liver tumors. Both tumor types are characterized by telomere shortening and reactivation of telomerase during carcinogenesis. Continuous cell proliferation, e.g., by oncogenic mutations, can cause extensive telomere shortening in the absence of sufficient telomerase activity, leading to dysfunctional telomeres and genome instability by breakage-fusion-bridge cycles, which induce senescence or apoptosis as a tumor suppressor mechanism. Telomerase reactivation is required to stabilize telomere functionality and for tumor cell survival, representing a genetic risk factor for the development of liver cirrhosis and liver carcinoma. Therefore, telomeres and telomerase could be useful targets in hepatocarcinogenesis. Here, we review similarities and differences between HCC and iCCA in telomere biology.

Impaired Myofibroblast Dedifferentiation Contributes to Nonresolving Fibrosis in Aging

Idiopathic pulmonary fibrosis (IPF) is a fatal age-associated disease with no cure. Although IPF is widely regarded as a disease of aging, the cellular mechanisms that contribute to this age-associated predilection remain elusive. In this study, we sought to evaluate the consequences of senescence on myofibroblast cell fate and fibrotic responses to lung injury in the context of aging. We demonstrated that nonsenescent lung myofibroblasts maintained the capacity for dedifferentiation, whereas senescent/IPF myofibroblasts exhibited an impaired capacity for dedifferentiation. We previously demonstrated that the transcription factor MyoD acts as a critical switch in the differentiation and dedifferentiation of myofibroblasts. Here, we demonstrate that decreased levels of MyoD preceded myofibroblast dedifferentiation and apoptosis susceptibility in nonsenescent cells, whereas MyoD expression remained elevated in senescent/IPF myofibroblasts, which failed to undergo dedifferentiation and demonstrated resistance to apoptosis. Genetic strategies to silence MyoD restored the susceptibility of IPF myofibroblasts to undergo apoptosis and led to a partial reversal of age-associated persistent fibrosis in vivo. The capacity for myofibroblast dedifferentiation and subsequent apoptosis may be critical for normal physiologic responses to tissue injury, whereas restricted dedifferentiation and apoptosis resistance in senescent cells may underlie the progressive nature of age-associated human fibrotic disorders. These studies support the concept that senescence may promote profibrotic effects via impaired myofibroblast dedifferentiation and apoptosis resistance, which contributes to myofibroblast accumulation and ultimately persistent fibrosis in aging.

Cellular senescence in vivo: From cells to tissues to pathologies

Senescent cells accumulate during aging in a variety of tissues. Although scarce, they could influence tissue function non-cell-autonomously via secretion of a range of factors in their neighborhood. Recent studies support a role of senescent cells in age-related morbidity, including neurodegenerative diseases, cardiovascular pathologies, cancers, aging-associated nephrological alterations, chronic pulmonary disease and osteoarthritis, indicating that senescent cells could represent an interesting target for therapeutic exploitation across a range of pathophysiological contexts. In this article, we review data available to indicate which cell types can undergo senescence within various mammalian tissue environments and how these processes may contribute to tissue-specific pathologies associated with old age. We also consider markers used to identify senescent cells in vitro and in vivo. The data discussed may serve as an important starting point for an extended definition of molecular and functional characteristics of senescent cells in different organs and may hence promote the development and refinement of targeting strategies aimed at removing senescent cells from aging tissues.

HBV induced hepatocellular carcinoma and related potential immunotherapy

Chronic infection of Hepatitis B virus (HBV) has long been recognized as a major risk factor in the initiation and development of hepatocellular carcinoma (HCC), contributing to over half the cases of HCC worldwide. Transformation of the liver with HBV infection to HCC mainly results from long-term interaction between HBV and the host hepatocytes via a variety of mechanisms, including HBV DNA integration, prolonged expression of the viral HBx regulatory protein and/or aberrant preS/S envelope proteins, and epigenetic dysregulation of tumor suppressor genes. While there have been several failures in the development of drugs for HCC, the immune-tolerant microenvironment of this malignancy suggests that immunotherapeutic agents could provide benefits for these patients. This is supported by recent data showing that immunotherapy has promising activity in patients with advanced HCC. In this review, we provide an overview of HBV-induced HCC and recent immune based approaches for the treatment of HCC patients.

Hepatocellular carcinoma prediction beyond year 5 of oral therapy in a large cohort of Caucasian patients with chronic hepatitis B

BACKGROUND & AIMS

Hepatocellular carcinoma (HCC) may develop in patients with chronic hepatitis (CHB) even after 5 years of oral therapy and cannot be easily predicted. We assessed predictors of HCC development and the need for HCC surveillance in this setting.

METHODS

Of 1,951 adult Caucasians with CHB included in the PAGE-B cohort, 1,427 (73%) had completed >5 years of follow-up under therapy without developing HCC by year 5. Median follow-up was 8.4 years from treatment onset. Points-based risk scores were developed to predict HCC risk after year 5.

RESULTS

In years 5-12, HCC was diagnosed in 33/1,427 (2.3%) patients with cumulative incidences of 2.4%, 3.2% and 3.8% at 8, 10 and 12 years, respectively. Older age or age >50 years, baseline cirrhosis and liver stiffness (LSM) ≥12 kPa at year 5 were independently associated with increased HCC risk. The HCC incidence was lower in non-cirrhotics than cirrhotics at baseline with year-5 LSM <12; among cirrhotics at baseline, it was lower in those with year-5 LSM <12 than ≥12 kPa. CAGE-B score was based on age at year 5 and baseline cirrhosis in relation to LSM at year 5 and SAGE-B score was based only on age and LSM at year 5 (c-index = 0.809-0.814, 0.805-0.806 after bootstrap validation). Both scores offered 100% negative predictive values for HCC development in their low risk groups.

CONCLUSIONS

In Caucasians with CHB, the HCC risk after the first 5 years of antiviral therapy depends on age, baseline cirrhosis status and LSM at year 5. CAGE-B and particularly SAGE-B represent simple and reliable risk scores for HCC prediction and surveillance beyond year 5 of therapy.

LAY SUMMARY

In Caucasians with chronic hepatitis B, the risk of hepatocellular carcinoma after the first 5 years of entecavir or tenofovir therapy depends on age, baseline cirrhosis status and liver stiffness at year 5, which can provide simple and reliable risk scores for hepatocellular carcinoma prediction and surveillance beyond year 5. In patients with cirrhosis at baseline, liver stiffness <12 kPa at year 5 is associated with lower HCC risk, but surveillance may be still required.

NADPH oxidases: Pathophysiology and therapeutic potential in age-associated pulmonary fibrosis

Oxidative stress has been associated with a number of human fibrotic diseases, including idiopathic pulmonary fibrosis (IPF). Although oxidative stress is associated with both fibrosis and aging, the precise cellular sources(s) of reactive oxygen species (ROS) that contribute to the disease pathogenesis remain poorly understood. NADPH oxidase (Nox) enzymes are an evolutionarily conserved family, where their only known function is the production of ROS. A growing body of evidence supports a link between excessive Nox-derived ROS and numerous chronic diseases (including fibrotic disease), which is most prevalent among the elderly population. In this review, we examine the evidence for Nox isoforms in the pathogenesis of IPF, and the potential to target this enzyme family for the treatment of IPF and related fibrotic disorders. A better understanding of the Nox-mediated redox imbalance in aging may be critical to the development of more effective therapeutic strategies for age-associated fibrotic disorders. Strategies aimed at specifically blocking the source(s) of ROS through Nox inhibition may prove to be more effective as anti-fibrotic therapies, as compared to antioxidant approaches. This review also discusses the potential of Nox-targeting therapeutics currently in development.